Use 1200 x 630 pixels, a 1.91 to 1 ratio, which is the size Facebook recommends for sharp previews and which crops well on LinkedIn, X and Slack. Serve it from a full https URL, keep important text away from the edges, and set twitter:card to summary_large_image so X shows it large.
Free link preview checker. See how your URL looks when shared on X (Twitter), LinkedIn, Facebook and Slack, and what is missing from your Open Graph and Twitter Card tags.
Open Social Media Link Preview Checker → Free toolFree Open Graph generator. Enter title, description, image and type to build valid og meta tags for rich link previews on Facebook, LinkedIn and Slack.
Open Open Graph Tag Generator →Link cards on the big platforms are wide rectangles close to 1.91 to 1. An image at 1200 x 630 fills that shape on high resolution screens without being upscaled, and smaller previews scale it down cleanly. Square or tall images get cropped, often cutting off a headline.
The image must be reachable by the crawler: a public https URL, not behind a login and not on a local or staging domain. Keep the file reasonably light so it loads in time, put the key words in the middle of the frame, and add og:image:width and og:image:height so platforms know the size before they download it.
You can, but most platforms will crop or shrink it, so a 1.91 to 1 image looks better in feeds.
Either works. JPG is usually smaller for photos; PNG keeps text and flat graphics sharp.
No. X reads og:image as a fallback; twitter:card set to summary_large_image makes it display large.